<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>渐变</title>
		<style>
			#a3{
				height: 400px;
				width: 400px;
				
				background-image: radial-gradient(red,blue,green,yellow);
				margin: 200px auto;
			}
			#a3:hover{
				border-radius: 50%; 
				transition: all 2s linear 0s;
				background-image: radial-gradient(pink,blue,green,red);
			}
		</style>
	</head>
	<body>
		<div id="a3">
			
		</div>
	</body>
</html>